I used to be able to play avi files on my Windows Media Player, but now I can’t. It says it doesn’t support those files or it doesn’t have the codecs for them. What do I need to do?
Get K-Lite Codec Pack
Some AVI container movies include audio that's readable by WMP, but some don't so maybe that's why you can't play them in WMP now. Getting K-Lite ensures you can play pretty much all AVI files in WMP. Read more about K-Lite and where to download it for free here.
Or you can install VLC to play all the file types that Windows Media Player doesn't play http://www.videolan.org/vlc/
That's what I do
AVI files are usually compressed with a non-Microsoft codec; the appropriate codec must be on your computer for the Player to play the file.
Get it here: